Angularly positioned marine propeller combination and a method of operating a marine propeller combination

Abstract

A marine propeller combination for a marine propulsion unit includes a first propeller and a second propeller arranged to rotate simultaneously in opposite directions about a common rotational axis. The marine propeller combination is configured such that the first and second propellers are angularly positioned such that during one revolution one of the blades of the first propeller is aligned with a drive leg of the marine propulsion unit when a blade gap of the second propeller is aligned with the drive leg, or one of the blades of the first propeller is aligned with the drive leg when one of the blades of the second propeller is aligned with the drive leg. The disclosure further relates to a marine vessel and to a method of operating a marine propeller combination.

The invention claimed is: 
     
         1 . A marine propeller combination, the marine propeller combination comprising a first propeller and a second propeller arranged to rotate simultaneously in opposite directions about a common rotational axis,
 the first propeller is adapted to be mounted on a first shaft of the marine propulsion combination and the second propeller is adapted to be mounted on a second shaft of the marine propulsion combination,   the first propeller comprises a first propeller position feature for angularly mounting the first propeller on the first shaft,   the second propeller comprises a second propeller position feature for angularly mounting the second propeller on the second shaft, and   the first propeller position feature is a visual marking or shape irregularity and the second propeller position feature is a visual marking or shape irregularity, wherein the first propeller position feature and the second propeller position features are arranged on the first and second propellers such that the first and second propellers are angularly positioned on the first and second shaft, respectively, such that during one revolution one of a plurality of blades of the first propeller is aligned with a drive leg of a marine propulsion unit when a blade gap of the second propeller is aligned with the drive leg, or   one of the plurality of blades of the first propeller is aligned with the drive leg when one of a plurality of blades of the second propeller is aligned with the drive leg.   
     
     
         2 . The marine propeller combination of  claim 1 , wherein one of the blades of the first propeller is aligned with the drive leg when the blade gap of the second propeller is aligned with the drive leg in a forward drive configuration of the marine propeller combination. 
     
     
         3 . The marine propeller combination of  claim 1 , wherein one of the blades of the first propeller is aligned with the drive leg when one of the blades of the second propeller is aligned with the drive leg in a rearward drive configuration of the marine propeller combination. 
     
     
         4 . The marine propeller combination of  claim 1 , wherein a number of propeller blades of the first propeller is three and a number of propeller blades of the second propeller is four. 
     
     
         5 . The marine propeller combination according to  claim 1 , wherein a number of propeller blades of the first propeller is four and a number of propeller blades of the second propeller is four, and the first and second propellers are angularly positioned such that when
 two of the blades of the first or second propeller are vertically oriented,   two of the blades of the other propeller are positioned angularly offset by 30 to 60 degrees with respect to a vertical axis.   
     
     
         6 . The marine propeller combination of  claim 1 , wherein the first propeller position feature is the shape irregularity in an internal spline pattern of the first propeller and/or the second propeller position feature is the shape irregularity in an internal spline pattern of the second propeller. 
     
     
         7 . The marine propeller combination according to  claim 1 , wherein the first propeller position feature is adapted for a first shaft position feature and the second propeller position feature is adapted for a second shaft position feature. 
     
     
         8 . A marine vessel comprising the marine propeller combination according to  claim 1 . 
     
     
         9 . The marine propeller combination of  claim 1 , wherein the shape irregularity is a lacking spline or a filled spline in an internal spline pattern. 
     
     
         10 . The marine propeller combination according to  claim 1 , wherein the first propeller position feature is the shape irregularity in an internal spline pattern of the first propeller and a corresponding first shaft position feature is a shape irregularity in an external spline pattern of the first shaft, and/or
 the second propeller position feature is the shape irregularity in an internal spline pattern of the second propeller and a corresponding second shaft position feature is a shape irregularity in an external spline pattern of the second shaft.   
     
     
         11 . A marine propulsion unit, comprising:
 a marine propeller combination and a drive leg supporting the marine propeller combination, wherein the marine propeller combination comprises a first propeller and a second propeller arranged to rotate simultaneously in opposite directions about a common rotational axis,
 the first propeller is adapted to be mounted on a first shaft of the marine propulsion unit and the second propeller is adapted to be mounted on a second shaft of the marine propulsion unit, 
 the first propeller comprises a first propeller position feature for angularly mounting the first propeller on the first shaft, 
 the second propeller comprises a second propeller position feature for angularly mounting the second propeller on the second shaft, and 
 the first propeller position feature is a visual marking or shape irregularity and the second propeller position feature is a visual marking or shape irregularity, 
   wherein the first propeller position feature and the second propeller position features are arranged on the first and second propellers such that the first and second propellers are angularly positioned on the first and second shaft, respectively such that during one revolution:
 one of a plurality of blades of the first propeller is aligned with a drive leg of a marine propulsion unit when a blade gap of the second propeller is aligned with the drive leg, or 
 one of the plurality of blades of the first propeller is aligned with the drive leg when one of a plurality of blades of the second propeller is aligned with the drive leg. 
   
     
     
         12 . The marine propulsion unit of  claim 11 , wherein
 the first propeller comprises the first propeller position feature and the first shaft comprises a corresponding first shaft position feature, said features being provided for angularly mounting the first propeller on the first shaft, and   the second propeller comprises the second propeller position feature and the second shaft comprises a corresponding second position feature, said features being provided for angularly mounting the second propeller on the second shaft.   
     
     
         13 . The marine propulsion unit of  claim 12 , wherein
 the first propeller position feature is the shape irregularity in an internal spline pattern of the first propeller and the first shaft position feature is a shape irregularity in an external spline pattern of the first shaft, and/or   the second propeller position feature is the shape irregularity in an internal spline pattern of the second propeller and the second shaft position feature is a shape irregularity in an external spline pattern of the second shaft.   
     
     
         14 . The marine propulsion unit of  claim 13 , wherein
 the shape irregularity in the external spline pattern of the first shaft comprises a filled spline, and/or   the shape irregularity in the external spline pattern of the second shaft comprises a filled spline.   
     
     
         15 . The marine propulsion unit according to  claim 11 , wherein the first shaft and the second shaft are arranged to rotate simultaneously in opposite directions at the same speed. 
     
     
         16 . A marine propulsion unit according to  claim 11 , the marine propulsion unit comprising the drive leg and the first shaft for the first propeller and the second shaft for the second propeller. 
     
     
         17 . The marine propulsion unit of  claim 16 , wherein
 the first shaft comprises a first shaft position feature corresponding to the first propeller position feature, said features being provided for angularly mounting the first propeller on the first shaft, and   the second shaft comprises a second position feature corresponding to the second propeller position feature, said features being provided for angularly mounting the second propeller on the second shaft.